The present invention relates to new and improved methods of removing volatiles, and particularly borates and flourides, from hot furnace gases.
In the manufacture of glass, fluxing materials are added to silica and/or high melting silicates, as for example the aluminum silicates, in order to produce an initial molten stage which hastens the dissolving of the silica and/or silicates; and in addition provides a manageable low melting temperature for the final glass product. Soda is an extensively used material for accomplishing these purposes; but soda by itself, produces glasses that are leachable in water and so have poor weathering characteristics. Soda glass is in fact so leachable that it cannot be used as the sole fluxing agent for glasses from which glass fibers are made; and so other fluxing materials, such as borates and/or flourides, are used to lower the melting temperature of the silicates, and provide silicates of sufficient low solubility in water that they have acceptable weathering characteristics. Glasses that contain borates and/or flourides, when in the molten stage, liberate borates and/or flourides, and these materials go out with the stack gases of the furnace. What is more, sodium borates and/or sodium flourides by themselves have appreciable vapor pressure at their melting temperatures so that a significant amount of these materials is lost when batches containing these materials are heated during the charging operation of glass furnaces. Borates and flourides produce ecological problems when they exit with stack gases; and so it has long been desired to find an economical way for extracting these volatile materials from the stack gases. It has been suggested heretofore that cooling air be mixed with stack gases to lower their temperature to the point where the volatile borates and fluorides condense into particulate matter which can be extracted from the gases by means of bag filters and/or electostatic precipitators. These methods of extraction are not economical, however, since the cooling air lowers the stack effect to such an extent that fans must be used to move the stack gases through the bag filters and/or electostatic precipitators. The cooling air that is introduced into the stack gases must be so voluminous, however, that the fan size becomes enormous, and the process uneconomical.
Prior to the present invention there has not been, to my knowledge, a process for extracting these volatiles from stack gases that is sufficiently simple, efficient, and economical to carry out, as to warrant commercial usage of the process.
An object of the present invention is the provision of a new and improved method of removing volatile borates and/or fluorides from the stack gases of glass furnaces, and the like.
Another object of the present invention is a new and improved process for preventing the escape of volatile borates and/or fluorides from batch materials during the time that the temperature of the batch materials is being raised to the temperature of complete fusion.
A further object of the present invention is the provision of a new and improved method of heating wet pellets of batch materials without destroying the pellets before they reach their molten stage.
Still further objects and advantages of the present invention will become apparent to those skilled in the art to which the invention relates from the following description of the preferred embodiments described with reference to the accompanying drawings forming a part of this specification.